My 580CK has the Cessna hydraulic pump which I have done the complete gasket, seal and spring/retaining ball rebuild twice but it keeps blowing out the main drive seal every time it takes on any amount of load. Tolerances are within specs in the manual. Any ideas would be greatly appreciated or if anyone knows of an aftermarket replacement pump it all would help. Thanks.
If the outlet pressure is in spec with no fluctuations the pump is worn out, gear teeth to housing, gear face to end plates, shaft bushings, shaft is grooved, etc. Most of the time gear pumps aren't worth doing
Recheck the check balls and that, any bypass oil that ends up in the seal area is supposed to drain off through whichever check ball passage is connected to the suction port. As mikebramel is saying, too much internal leakage and the bleed off passage can't keep up.
Thanks guys, I will have another look at the check ball passage before getting a new pump but it looks like she has done her time.